: The investigators and others have previously demonstrated that CsA and more recently tacrolimus (Tac) induce transforming growth factor beta (TGF-B). A number of studies have demonstrated that TGF-B is both immunosuppressive and fibrogenic. Recently, they demonstrated that TGF-B mimics and anti-TGF-B abrogates both the anti-proliferative and fibrogenic effects of CsA in a non-transplant short-term in vivo mouse model. Cell-cycle arrest appears to be at least one main feature of the efficacy of immunosuppressive drugs, and TGF-B has been reported to induce the expression of one cell cycle inhibitor, p21. The investigators' that this phenomenon may be TGF-B- independent. If confirmed, these intriguing findings would suggest a potential dichotomy between at least some of the immunosuppressive properties of these agents and their fibrogenic effects, thus providing targets for pharmacologic modification to enhance or diminish specific properties. The current hypothesis based on these newer findings is that the efficacy of CsA and Tac is multifactorial and, in addition to the effects on TGF-B and IL-2, directly induces cell cycle inhibitors such as p21. The investigators also propose that the primary toxic effects of CsA and Tac are via the induction of TGF-B, which then induces fibrogenic genes including collagen and fibronectin. Accordingly, the specific aims of this proposal are 1) To determine whether the efficacy of CsA and Tac are dependent on TGF-B, p21 or both, using the complete MHC mismatch rat heart transplant model, which requires chronic immunosuppression to prevent rejection. The investigators will use antibodies to TGF-B and p21 alone or in combination to determine whether acute rejection is accelerated in CsA and Tac treated animals within the first 30 days post-transplant. 2) To further dissect the interaction between CsA and Tac, TGF-B and p21, using in vitro studies on A-549 cells that are either unmodified or are TGF-B- or p21-deficient. The effect of CsA and Tac on the stimulation of promoter activity of p21 gene will be studied using TGF-B inducible and non-inducible promoter constructs made chimeric with luciferase reporter gene. 3) To determine whether the nephrotoxicity of CsA and Tac are secondary to TGF-B. In non-transplanted animals treated with CsA or Tac over 3-6 months, the investigators will use anti-TGF-B antibodies to attempt to abrogate the nephrotoxic effects. Also, to determine the time course of the induction of TGF-B1 and the ECM genes collagen and fibronectin, they will investigate the induction of these genes by CsA and Tac in glomerular mesangial cells and proximal tubular epithelial cells in vitro. These studies will directly determine the role (if any) of the TGF-B and/or p21 pathways in the efficacy, and TGF-B in the toxicity, induced by CsA and tacrolimus.